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Adiabatic connection forms in density functional theory: H(2) and the He isoelectronic series

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Article numberARTN 064105
<mark>Journal publication date</mark>14/08/2008
<mark>Journal</mark>Journal of Chemical Physics
Issue number6
Number of pages7
<mark>Original language</mark>English


Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing two challenging problems in density functional theory-the singlet ground state potential energy curve of H(2) in a restricted formalism and the energies of the helium isoelectronic series, H(-) to Ne(8+). For H(2), an exponential-based form yields a potential energy curve that is virtually indistinguishable from the FCI curve, eliminating the unphysical barrier to dissociation observed previously with a [1,1]-Pade-based form and with the random phase approximation. For the helium isoelectronic series, the Pade-based form gives the best overall description, followed by the exponential form, with errors that are orders of magnitude smaller than those from a standard hybrid functional. Particular attention is paid to the limiting behavior of the AC forms with increasing bond distance in H(2) and increasing atomic number in the isoelectronic series; several forms describe both limits correctly. The study illustrates the very high quality results that can be obtained using exchange-correlation functionals based on simple AC forms, when near-exact data are used to determine the parameters in the forms. (C) 2008 American Institute of Physics.